Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical wireless network includes a number of base stations each radiating to provide coverage in which to serve wireless communication devices (WCDs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a WCD within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a wireless network may operate in accordance with a particular air interface protocol (i.e., radio access technology), with communications from the base stations to WCDs defining a downlink or forward link and communications from the WCDs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, wireless wide area network (WWAN) protocols such as Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), and wireless local area network (WLAN) protocols such as IEEE 802.11 (WIFI), BLUETOOTH, and others. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In practice, a base station may be configured to provide service to WCDs on multiple carrier frequencies or “carriers.” Each carrier could be a time division duplex (TDD) carrier that defines a single frequency channel multiplexed over time between downlink and uplink use, or a frequency division duplex (FDD) carrier that defines two separate frequency channels, one for downlink communication and one for uplink communication. Each frequency channel of a carrier may then occupy a particular frequency bandwidth (e.g., 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, or 20 MHz) defining a range of frequency at a particular position (e.g., defined by a center frequency) in a radio frequency band (e.g., in the 800 MHz band, the 1.9 GHz band, or the 2.5 GHz band).
Each carrier may also define various logical channels to facilitate communication between the base station and one or more served WCDs. For instance, on the downlink, a carrier may define a reference channel on which the base station broadcasts a reference signal useable by WCDs to detect and evaluate coverage, various other downlink control channels to carry control signaling (such as resource-scheduling directives) to WCDs, and one or more shared or traffic channels for carrying bearer data (e.g., user or application level data) to WCDs. And on the uplink, a carrier may define one or more uplink control channels to carry control signaling (such as resource scheduling requests, channel state reports, and the like) from WCDs, and one or more shared or traffic channels for carrying bearer data from WCDs. In practice, the shared or traffic channels may define particular physical resources for carrying data between the base station and WCDs.
When a WCD enters into coverage of a base station, the WCD may attach, register, or otherwise associate with the base station, and the base station may then serve the WCD on one or more carriers. In practice, the process of serving the WCD may involve the base station allocating use of particular air interface resources, such as traffic channels or portions thereof, to carry data communications to and from the WCD, and managing transmission on those resources, such as controlling what modulation scheme is used for the transmissions.
For instance, when the base station has data to transmit to the WCD, the base station may select certain downlink resources to carry the data and may determine a modulation scheme for transmission on those resources, and the base station may then (i) transmit to the WCD a scheduling directive instructing the WCD to receive the data on the scheduled resources using the determined modulation scheme, and (ii) transmit the data on the indicated downlink resources using the determined modulation scheme. Likewise, when the base station receives from the WCD a request for the WCD to transmit data to the base station, the base station may select certain uplink resources to carry the data and may determine a modulation scheme for transmission on those resources, and the base station may then (i) transmit to the WCD a scheduling directive instructing the WCD to transmit the data on the scheduled resources using the determined modulation scheme and (ii) receive the transmission from the WCD accordingly.
To efficiently serve a WCD, a base station may keep track of the WCD's channel state, such as the WCD's downlink signal strength and quality and the WCD's radio/antenna configuration, and may set or adjust service parameters for the WCD accordingly. By way of example, the base station could use the WCD's channel state as a basis to select an appropriate modulation scheme or transmission format to use for transmission to or from the WCD. For instance, the base station could select a higher-order modulation scheme if the channel state is relatively good and a lower-order modulation scheme if the channel state is relatively poor, as a lower order modulation scheme may be more reliable than a higher order modulation scheme in poor channel conditions.
To facilitate this in practice, each WCD served by the base station may periodically determine and report its channel state to the base station, at regular intervals according to a defined channels state reporting rate. For instance, each WCD may periodically establish one or more channel state metrics based downlink signal strength measurements and radio/antenna configuration and generate and transmit one or more associated channel state reports to the base station. The WCDs may transmit these channel state reports to the base station on uplink signaling channels and/or uplink traffic The base station may thus receive these reports and keep a record of each WCD's latest indicated channel state, so that the base station can set or adjust its service of the WCD accordingly.